Biologic drugs account for a disproportionate share of the increase in pharmaceutical spending in the US and worldwide. Against this backdrop, many look to the expanding market for biosimilars-follow-on products to biologic drugs-as a vehicle for controlling pharmaceutical spending. This study explores the early years of entry of biosimilars and related follow-on products in the US. Using monthly sales data from the period 2005-19 for ten drug classes, we examine how quickly biosimilars/follow-on products gained market share and the subsequent trajectory of prevailing (national average invoice) prices. Our analysis suggests that although uptake has been slower than what is typically seen in generic drug markets, the most recent entrants have captured market share more rapidly than comparable earlier biosimilars/follow-on products. We also document that from biosimilar/follow-on products' time of entry, their lower prices help offset the overall trend in average annual reference-product price increases. Our findings can provide insight into future policy reforms aimed at increasing competition and use of biosimilars, leading to expanded patient access and significant cost savings.